When illuminating a parking lot, a street or even the inside of a building, it is oftentimes desirable to provide generally uniform illumination over the target area. Designers of parking lots, streets and buildings typically specify a minimum illuminance (lumens per square foot or meter) required throughout the target area. The illuminance at locations on the target area that exceeds the specified minimum can be considered as wasted illuminance. It is desirable to redirect the light that would have been directed toward areas that exceed the minimum illuminance to reduce the amount of energy required to illuminate the entire target area.
Illumination is inversely proportional to the square of the distance between the point light source and a point on the surface that is to be illuminated, i.e. the target area. Because of this law, a light fixture placed x distance (feet or meters) above a planar target area will require eight times the luminous intensity in a direction that is offset 60° from the vertical axis as compared to the light output in the vertical axis in order to provide the same illuminance at each location on the plane. Known light sources, incandescent and arc type lamps, account for this by designing a reflector that directs more light toward the periphery of the target area. This design can be accomplished by assuming that the incandescent or arc type light source is a point light source and then appropriately shaping the reflector to accommodate this point light source.
Light emitting diodes (“LEDs”), on the other hand, are typically not powerful enough so that a single LED, which could act as the point light source similar to the incandescent and arc type lamps, provides sufficient illumination over a large target area. This is especially the case where the LED is positioned several feet or meters above the target area. Moreover, LEDs typically do not emit light in a spherical pattern, such as incandescent and arc-type lamps, thus making it difficult to design an appropriate reflector.
To provide sufficient illumination for the target area multiple LEDs can be required to provide the sufficient amount of lumens to provide the minimum illuminance to meet the project specifications for the target area. LEDs are typically mounted on a printed circuit board (“PCB”) and when a sufficient amount of LEDs are provided on the PCB, however, the size of the PCB required and the number of LEDs required makes it difficult to consider the plurality of LEDs in aggregate as a single point light source. In view of this, it has been known to provide separate optics, either refractive of reflective, for each LED to redirect the light emanating from each LED. Providing a separate optic for each LED can be expensive and also make design of the fixture difficult, especially where it is desirable to provide a light fixture that is easily scalable so that it can be used in a number of different applications. Additionally, the number of LEDs that are required to meet illuminance specifications and the spacing required between adjacent LEDs can result in a very large light fixture.